Add Solidify Modifier to a plane with a different image on each side
When you use the solidify modifier, you are giving the object &quot;faces&quot; with their normals pointed outwards. This means that in the new &quot;box&quot; you create, all the &quot;backfacing&quot; faces are facing the inside (so you cant see them). You can either apply the modifier and add a different material for the different faces (as desired), or you could select the face you want to be different and flip the normals on it.